The present invention relates generally to the field of liquid entrapment and draining devices, and more particularly to an apparatus for automatically removing liquid from a pressurized gas system such as one used in the pulmonary ventilation of human patients.
In a pressurized gas system, particularly where the gas is intentionally humidified, water or other liquid accumulates in the gas-carrying conduits of the system due to condensation or other effects. Such accumulations can have a deleterious effect on the functioning of the system. This is especially a problem in medical ventilator systems, which typically require the humidification (up to 100% relative humidity at body temperature) of the inspiratory gas, and which must accommodate high moisture content expiratory gas. In medical ventilator systems, excessive moisture accumulations can be counterproductive to the effective treatment of the patient, and it is therefore necessary to remove accumulated liquid from the patient circuit on a regular and frequent basis.
the most common approach to removing liquid accumulating in the patient circuit of a ventilator has been to disconnect the ventilator from the patient and then manually empty the liquid (typically saliva, sputum, and condensed water vapor from the humidifier), accumulated in the patient circuit conduits, into an open container. This may cause discomfort to the patient, and may expose the attendant or others to possibly infectious materials in the liquid. Furthermore, this procedure requires regular attention and a significant amount of labor.
Other approaches to the problems of condensate accumulation have included the metering of the amount of water introduced by the humidification system into the ventilator circuit by a servo-controlled water feed, and the insertion of heater wires into the patient circuit tubing to reduce the amount of condensation. These approaches have met with varied success. In any case, the servo-controlled water feed systems suffer from significantly increased cost and complexity, while the heater wires introduce flow resistance to a patient circuit, which is undesirable, especially in the small bore tubes used with neonatal patient circuits.
Drain valves or water traps such as those shown in U.S. Pat. No. 4,867,153 and 4,457,305 rely on complicated and/or unique liquid storage containers and introduce a significant volume into the patient circuit. This increase in patient circuit volume results in an increase in the system's pneumatic compliance, which is always undesirable, but particularly unacceptable in a patient circuit used for an infant.
While other drain valves have been developed for removing liquid from other forms of pressurized gas systems (see, e.g., U.S. Pat. No. 2,007,358, 2,100,485 and 2,125,144), they tend toward complex and expensive mechanisms, such as solenoid-actuated valves or tapered valve seats. In many instances, they may also significantly increase the volume in the pressurized gas circuit.
From cost, convenience, and anti-contamination standpoints, it would be desirable to have a drain valve that works automatically, and is inexpensive and disposable. Such a valve should also be adaptable for use with existing ventilator circuits, without significantly increasing either the volume of the circuit or its pneumatic resistance. Such a valve should also allow entrapment and drainage of the condensate without direct exposure to the atmosphere or to those attending the patient.